This invention relates generally to the field of rotating magnetic storage devices, and more particularly to improved means and methods for increasing the reliability of a magnetic disk storage system in which a plurality of mechanically coupled, but separately driven magnetic head actuators are employed in a head/disk assembly.
A head/disk assembly typically comprises one or more commonly driven magnetic disks rotatable about a common spindle and cooperating with at least one head actuator for moving a plurality of heads radially relative to the disks so as to provide for the reading and/or writing of data on selected circular tracks provided on the disks. Where a plurality of head actuators are employed, they are located at different circumferential positions relative to the disks. Also, in order to obtain greater system flexibility, it is advantageous to provide for each head actuator to be separately controllable so that its respective heads can be moved to a desired track irrespective of the track position provided by any other head actuator for its respective heads.
Where a plurality of separately controllable head actuators are provided, they are typically mounted on a common (or mechanically interconnected) base structure. Thus, the driving of one head actuator will cause at least some portion of the mechanical driving forces to be coupled to other head actuators via the common base structure. A head/disk assembly and its associated servo control are typically constructed and arranged so that coupling forces produced as a result of driving a head actuator does not deleteriously affect the operation of any other head actuator.
However, because of the demand for greater data storage density and faster access speed in a disk storage system, head/disk assemblies are being designed with reduced track-to-track spacings to increase density and larger actuator driving forces to reduce access time. As a result, the driving forces coupled from one head actuator to another are that much more difficult to handle. For example, it has been found that when a head actuator is to be driven an appreciable radial distance, the large driving force required to provide rapid access may cause a sufficiently large force to be coupled to another head actuator so as to displace its heads off their current track by an amount which cannot be compensated for by the servo control. Of course, it may be possible to redesign the mechanical structure of the head/disk assembly and/or the servo control circuitry to prevent this from happening, but the expense will be considerable, particularly since redesign typically requires extensive testing and field experience to insure reliability.